1. Field of the Invention
This invention relates to gas turbine engines, and specifically to gas turbine engines that produce very high airflow through the fan portion thereof.
2. Background of the Invention
In typical aircraft gas turbines engines, a fan is used upstream of the low compressor to maximize the amount of thrust that an engine can produce for a given rate of fuel consumption. By increasing the size of the fan, the thrust produced by an engine can be significantly increased without significantly increasing the fuel consumption of the engine. Therefore, designers of aircraft gas turbine engines have typically increased the diameter of the fan on gas turbine engines whenever the need for additional thrust has occurred.
However, as the diameter of fans have become larger, engine designers have encountered several problems. One problem is that, as the individual fans blades become longer, the thickness of each blade must be increased to handle the additional centripetal force generated by the longer blade. As a result, blades must become heavier to be made from the same materials to handle the additional loading in each blade at the root and platform thereof, or the blades must be manufactured from lighter, more expensive materials. Since one of the goals of designers of aircraft gas turbine engines is to minimize both weight and cost, neither of these options is considered to be desirable.
Another problem is that the diameter of blades on some engines has reached the point where the speed of the tips of the fan blades are near supersonic. If the tip speeds should become supersonic, additional stresses would be introduced into the blades, and therefore the blades would have to be redesigned to tolerate such additional stresses. This type of redesign would require expensive design and testing, which would further increase the cost of higher thrust aircraft engines.
An additional problem is that as the length of each blade increases, it becomes more difficult to design the blade so that it flows air efficiently along its full length, because the relative speed of each blade adjacent to root thereof is much slower than the speed of the blade adjacent the tip thereof. And as the diameter of the fan increases, the ground clearance for wing mounted engines must be increased to prevent the engine nacelles from impacting the runway during takeoffs and landings.
What is needed is means for increasing airflow through the fan portion of a gas turbine engine without increasing the diameter of the fan.
It is therefore object of the present invention to provide a means for increasing airflow through the fan portion of a gas turbine engine without increasing the diameter of the fan.
Accordingly, the present invention provides a ducting system for use on a gas turbine engine having two fans connected to a common shaft, and includes a primary inlet duct that is integral with a plurality of primary discharge ducts, a plurality of secondary inlet ducts that are integral with a secondary discharge duct, each of the ducts includes a port, the ports of the secondary inlet ducts are located radially outward of the port of the primary inlet duct, and the ports of the primary discharge ducts are located radially outward of the port of the secondary discharge duct.
The foregoing and other features and advantages of the present invention will become more apparent from the following description and accompanying drawings.